Three highly divergent groups of Plum pox virus strain D isolates coexist in stone-fruit plantings of Nikita Botanical Gardens, Crimea

摘要

Nikita Botanical Gardens are located in the subtropical area of the Crimean peninsula. Thousands of both local and introduced cultivars and hybrid forms of peach, nectarine, apricot, plum and myrobalan are maintained in the Prunus collections of the Gardens. Surveys of stone-fruit plantings using double antibody sandwich ELISA and RT-PCR resulted in the finding of numerous Plum pox virus (PPV) isolates belonging to strain D (PPV-D). Phylogenetic analysis of the (Cter)NIb-CP-3'NCR genomic region revealed three distinct, highly divergent groups of isolates. Most of them were found in the peach, nectarine and plum collections, as well as on wild myrobalan {Prunus cerasifera) trees growing among collection plantings. Together with the Hungarian isolatesSoscutl and Szigetcsepl, they form a monophyletic cluster distinct from PPV-D isolates from all other localities in Crimea and beyond, as supported by high bootstrap values. This cluster could have evolved from an East European predecessor, which led tothe emergence of several distinct but related isolates. Isolate K27, found in the myrobalan collection, clustered separately from the other Crimean isolates, suggesting another independent PPV introduction into the Gardens. Three more distinct isolates,found on wild myrobalan trees outside the collections, were very distantly related to other Crimean isolates and to those from the rest of the world. Of all currently known PPV-D isolates, they are probably the closest to the putative ancestor of this strain. These isolates could have reached the Crimea with the introduction of PPV-infected cultivated forms of myrobalan from the Trans-Caucasian region, which is completely unexplored in relation to PPV incidence and genetic diversity.